Human birth defects and cancers are often caused by misregulation of the Wnt signaling pathway. In early vertebrate embryos, development of the body axis critically requires the activation of the Wnt pathway on one side of the embryo. In the frog Xenopus, a predominant model organism for axis formation, asymmetric Wnt signaling is achieved by the differential localization of maternally derived molecules stored in the egg. These determinants are translocated toward the future dorsal side by microtubule-based rotational movements of the egg cortex following fertilization. Interference with this process results in embryos lacking the dorsal tissues. The exact mechanisms regulating asymmetry in cortical rotation and Wnt activation in axis formation remain unclear. Data from maternal loss-of- function studies, including preliminary studies for this proposal, have implicated vegetally localized factors. The long-term goal of this research is to understand the role of these localized maternal gene products in embryonic axis formation. Preliminary studies for this proposal have identified a potential for maternal Wnt signals in regulating cortical rotation. Novel methods for monitoring microtubule dynamics during cortical rotation in vivo are also employed. The objectives of this proposal are to determine mechanisms underlying the formation of the vegetal microtubule array and to characterize potential determinants carried on the array. The specific aims are to determine the roles of localized mRNAs in controlling microtubule assembly during the cortical rotation, to determine the extent this process is regulated by ongoing Wnt signaling in the oocyte and to characterize protein determinants in the vegetal cortex.